Equal_HashCode_TEST --- imporatnt concept about hashing, Java

Equal_HashCode_TEST --- imporatnt concept about hashing

//'main' method must be in a class 'Rextester'.

import java.util.*;
import java.lang.*;

// abstract so -> can't make its object
abstract class Element {
    int intVal;
    double doubleVal;
    String stringVal;

Element(final int intVal, final double doubleVal, final String stringVal) {
        this.intVal = intVal;
        this.doubleVal = doubleVal;
        this.stringVal = stringVal;
    }
}

class Element_Overridden extends Element {

Element_Overridden(final int intVal, final double doubleVal, final String stringVal) {
        super(intVal, doubleVal, stringVal);
    }

@Override
    public boolean equals(Object obj) {
        Element_Overridden e = (Element_Overridden) obj; // DOWNCASTING

if (this.intVal == e.intVal && this.doubleVal == e.doubleVal && this.stringVal.equals(e.stringVal))
            return true;
        else
            return false;
    }

@Override
    public int hashCode() {
        return this.intVal;
    }

}

class Element_NOT_Overridden extends Element {

Element_NOT_Overridden(final int intVal, final double doubleVal, final String stringVal) {
        super(intVal, doubleVal, stringVal);
    }
}

class Rextester {

public static void main(String[] args) {
        test_Element_Overridden();
        test_Element_NOT_Overridden();
    }

public static void test_Element_NOT_Overridden() {
        System.out.println("\n\n\n\t -- TEST :  NOT OVERRIDDEN -- \n");

HashSet<Element_NOT_Overridden> hSet = new HashSet<>();
        hSet.add(new Element_NOT_Overridden(1, 23, "first"));
        hSet.add(new Element_NOT_Overridden(2, 62, "second"));
        hSet.add(new Element_NOT_Overridden(3, 25, "third"));

// --> NOTE : we have fucked with the intVal parameter --> IMPORTANT CONCEPT
        hSet.add(new Element_NOT_Overridden(1, 53, "fifth"));
        hSet.add(new Element_NOT_Overridden(2, 235, "sixth"));

System.out.println("\n" + hSet);

printSet(hSet);

// NOTE : although all the above objects are different
        // but there hashcode could be same --> Lets SEE.

// NOTE : all the elements in it are upcasted to Element
        // --> as to make only one general method :: SO need manual DownCasting now
        ArrayList<Element> list = setToArrayList(hSet);

for (int i = 0; i < list.size(); i++) {
            Element_NOT_Overridden el = (Element_NOT_Overridden) list.get(i); // NEED DOWNCASTING NOW

for (int j = 0; j < list.size(); j++) {
                Element_NOT_Overridden tempEl = (Element_NOT_Overridden) list.get(j); // NEED DOWNCASTING NOW

System.out.print("\n\n" + el + "  -vs-  " + tempEl);

if (el == tempEl)
                    System.out.print("\t--------> NOTICE : same hascode : but then also NOT EQUAL is possible");

System.out.print("\n" + elementToString(el) + "  -vs-  " + elementToString(tempEl));

if (el.equals(tempEl)) {
                    System.out.println("\t\t\t\t====>>>>  EQUAL");
                } else {
                    System.out.println("\t\t\t\t====>>>>  NOT - EQUAL");
                }
            }
            System.out.println("\n| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | ");
        }

}

public static void test_Element_Overridden() {
        System.out.println("\n\n\n\n\n\n\t -- TEST :   OVERRIDDEN -- \n");

HashSet<Element_Overridden> hSet = new HashSet<>();
        hSet.add(new Element_Overridden(1, 23, "first"));
        hSet.add(new Element_Overridden(2, 62, "second"));
        hSet.add(new Element_Overridden(3, 25, "third"));

// --> NOTE : we have fucked with the intVal parameter --> IMPORTANT CONCEPT
        hSet.add(new Element_Overridden(1, 53, "fifth"));
        hSet.add(new Element_Overridden(2, 235, "sixth"));

System.out.println("\n" + hSet);

printSet(hSet);

// NOTE : although all the above objects are different
        // but there hashcode could be same --> Lets SEE.

// NOTE : all the elements in it are upcasted to Element
        // --> as to make only one general method :: SO need manual DownCasting now
        ArrayList<Element> list = setToArrayList(hSet);

for (int i = 0; i < list.size(); i++) {
            Element_Overridden el = (Element_Overridden) list.get(i); // NEED DOWNCASTING NOW

for (int j = 0; j < list.size(); j++) {
                Element_Overridden tempEl = (Element_Overridden) list.get(j); // NEED DOWNCASTING NOW

System.out.print("\n\n" + el + "  -vs-  " + tempEl);

if (el == tempEl) {
                    System.out.print(
                            "  ---> NOTICE : same hascode - so same but see there are obj with same code BUT THEN also NOT EQUAL \n\t\t\t but NOTE: this means the representation ClassName@Code  is not actual value of reference : its just representation, \n\t\t\twhich is used when you have not imlemented the toString() method of that class");
                } else if(el.hashCode() == tempEl.hashCode()){
                    System.out.print("\t\t <<--- SEE");
                }

System.out.print("\n" + elementToString(el) + "  -vs-  " + elementToString(tempEl));

}

// NOTE : they both inherit Elements ---> upcasting
    public static void printSet(Set set) {
        System.out.print("\n  [[[ ");
        for (Object obj : set) {

Element e = (Element) obj;// DOWNCASTING
            System.out.print(e.intVal + "-" + e.stringVal + "-" + e.doubleVal + "  |  ");
        }
        System.out.println("]]] ");

}

public static ArrayList<Element> setToArrayList(Set set) {
        ArrayList<Element> aList = new ArrayList<>();

for (Object o : set) {
            Element e = (Element) o; // DOWN-CASTING
            aList.add(e);
        }
        return aList;
    }

// upcasting for both the classes : Element_NOT_Overridden && Element_Overridden
    public static String elementToString(Element e) {
        return (e.intVal + "-" + e.stringVal + "-" + e.doubleVal + "  ");
    }
}


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